After the introduction of offset printing of newsprint at the beginning of the 1970's, it became possible for newspapers to print in four colors. In order to be acceptable to advertisers, who contribute to the finances of newspapers, four-color newspapers need to be printed on much better paper than necessary without four-color printing. The main criteria are reduced print-through of printing ink, greater whiteness and a sufficiently high coefficient of friction of the paper surface.
Reduced print-through is necessary because the paper goes through a printer not once but four times. A high degree of whiteness is necessary if four-color printing is to be possible at all. The coefficient of friction has to be sufficiently high to prevent slipping in the printing press and thus ensure the register which is so important for four-color printing.
In North America and Scandinavia, newsprint paper is conventionally made from virgin fibers. TMP fibers are used in Scandinavia, and considerable quantities of mechanical wood pulp in Canada. This means it is necessary to include cellulose in the formulation to obtain the required strength. A common feature of these methods, until recently, was substantial non-use of waste paper. In Central Europe this goes back to a long tradition including newsprint paper.
Admittedly, newsprint-paper manufacturers in Scandinavia and in the USA and Canada are making increased use of waste paper, encouraged in North America by Government intervention by legislation in the principal states in the USA. In these regions, however, pristine fibers will never lose their fundamental importance, if only because pristine fibers always have to be introduced for technical reasons even if fiber recycling is intensified.
The higher the pristine fiber content, the more urgent is the need, given the nature of the demand for newsprint paper as described above, to reduce the print-through to an acceptable amount, owing to the absence of fillers inevitably supplied via the waste paper. Normally print-through is reduced by increasing the opacity of the paper, i.e. increasing the weight per unit area or the content of pigment, and consequently a necessary proportion of fillers is desirable to a certain extent, to give subsequent strength to the paper. This does not--or to a decreasing extent, relieve paper manufacturers of the need at least to think about deliberate incorporation of fillers which are not supplied via waste paper. This will be essential if no waste paper is used. This is confirmed by the reaction of the Swedish paper industry.